The present invention relates to a spot killer circuit for the television receiver which may completely prevent a picture tube from being burned after a power switch is turned off.
In various equipment incorporating picture tubes such as television receivers, display monitors and so on, when the charge still remains on the picture tube after the power switch is turned off, the beam current flows due to the residual heat of the heater of the picture tube even after the deflection system stops its operations so that spots are produced on the screen of the picture tube. When the beam current is high, the intensified spot impinges on the phosphor screen, thus causing a spot damage to it. In order to overcome this problem, there has been devised and demonstrated a spot killer circuit of the type in which the bias voltage of the picture tube is brought to zero at the instant when the power switch is turned off, thereby causing the discharge of the picture tube. However when the extremely high voltage system has a high capacitance, the discharge of the picture tube will not be completed before the operations of the deflection system stop so that a spot is still produced.